It appears that the moose eventually realized that the warden was trying to help him.

I think we as humans give animals too much credit for higher level thinking.
The moose was in shock. Did you see the heavy breathing? The beast was exhausted. I don't believe it was a matter of the moose understanding that the GW was helping but rather an instinctive matter,built-in primitive brain stem features if you will...like "don't move when you're in shock and 'trapped'.